6.8	UVIS Sensitivity

6.8.1 Limiting Magnitudes

6.8.1 Limiting Magnitudes

Table 6.10 presents the predicted limiting-magnitude performance of WFC3 and compares it with that of the ACS camera. The calculations are based on optimal extraction of a point source. The limiting ABMAG at a S/N of 10 was calculated for a 1-hour and a 10-hour exposure. The WFC3 filters used are listed in column 2; for ACS, the most comparable wide-band filter was used and its name is given in column 3. The ACS/HRC camera was assumed for the NUV and U-band comparison, and ACS/WFC was assumed for B, V, and I.

Table 6.10: Limiting-magnitude performance of WFC3 compared with that of ACS based on on-orbit sensitivity from SMOV4. The table provides limiting ABMAGs at a S/N of 10 for the indicated WFC3 filters and for ACS with its most similar filters. WFC3 UVIS comparisons are with the now inoperable ACS HRC channel (NUV and U) and the ACS WFC channel (B,V,I).

Band	Filter			Limiting magnitude in 1 hr			Limiting magnitude in 10 hrs
	WFC3	ACS		WFC3	ACS		WFC3	ACS
NUV	F225W	F220W (HRC)		26.7	25.9		28.1	27.2
U	F336W	F330W (HRC)		27.3	26.4		28.7	27.8
B	F438W	F435W (WFC)		27.3	27.6		28.7	28.9
V	F606W	F606W (WFC)		27.9	27.9		29.2	29.2
I	F814W	F814W (WFC)		27.1	27.4		28.4	28.7

Chapter 9 gives further details on estimation of exposure times. More accurate estimates require use of the WFC3 Exposure Time Calculator (ETC), available online.